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From Marc Prud'hommeaux <mprud...@apache.org>
Subject Re: Using DDL generation in a Java EE environment?
Date Fri, 16 Mar 2007 17:26:52 GMT
Marina-

On Mar 15, 2007, at 5:01 PM, Marina Vatkina wrote:

> Hi,
>
> I am part of the GlassFish persistence team and was wondering how  
> does OpenJPA support JPA auto DDL generation (we call it "java2db")  
> in a Java EE application server.
>
> Our application server supports java2db via creating two sets of  
> files for each PU: a ...dropDDL.jdbc and a ...createDDL.jdbc file  
> on deploy (i.e. before the application  is actually loaded into the  
> container) and then executing 'create' file as the last step in  
> deployment, and 'drop' file on undeploy or the 1st step in  
> redeploy. This allows us to drop tables created by the previous  
> deploy operation.
>
> This approach is done for both, the CMP and the default JPA  
> provider. It would be nice to add java2db support for OpenJPA as  
> well, and I'm wondering if we need to do anything special, or it'll  
> all work just by itself?

We do have support for runtime creation of the schema via the  
"openjpa.jdbc.SynchronizeMappings" property. It is described at:

   http://incubator.apache.org/openjpa/docs/latest/manual/ 
manual.html#ref_guide_mapping_synch

The property can be configured to run the mappingtool (also described  
in the documentation) at runtime against all the registered  
persistent classes.


> Here are my 1st set of questions:
>
> 1. Which API would trigger the process, assuming the correct values  
> are specified in the persistence.xml file? Is it:
> a) <provider>.createContainerEntityManagerFactory(...)? or
> b) the 1st call to emf.createEntityManager() in this VM?
> c) something else?

b


> 2. How would a user drop the tables in such environment?

I don't think it can be used to automatically drop then create  
tables. The "mappingtool" can be executed manually twice, the first  
time to drop all the tables, and the second time to re-create them,  
but I don't think it can be automatically done at runtime with the  
"SynchronizeMappings" property.


> 3. If the answer to either 1a or 1b is yes, how does the code  
> distinguish between the server startup time and the application  
> being loaded for the 1st time?

That is one of the reasons why we think it would be inadvisable to  
automatically drop tables at runtime :)


> 4. Is there a mode that allows creating a file with the jdbc  
> statements to create or drop the tables and constraints?

Yes. See:

   http://incubator.apache.org/openjpa/docs/latest/manual/ 
manual.html#ref_guide_ddl_examples


> thank you,
> -marina
>


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